CN102986144B - For sending and receive the method for multi-carrier signal, corresponding transmitter and receiver - Google Patents
For sending and receive the method for multi-carrier signal, corresponding transmitter and receiver Download PDFInfo
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- CN102986144B CN102986144B CN201180034308.2A CN201180034308A CN102986144B CN 102986144 B CN102986144 B CN 102986144B CN 201180034308 A CN201180034308 A CN 201180034308A CN 102986144 B CN102986144 B CN 102986144B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
- H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
- H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
- H04B7/0621—Feedback content
- H04B7/0626—Channel coefficients, e.g. channel state information [CSI]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
- H04L25/0204—Channel estimation of multiple channels
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Abstract
The present invention relates to a kind of for by using the transmitter of at least two transmission antennas to the method using at least one receiver of at least one reception antenna to send multi-carrier signal, comprising the step of the estimation for obtaining at least one downlink transport channel.According to the present invention, such method comprises transfer phase, for realizing the iteration at least one times of following steps at least one downlink channel: when considering the estimation of described downlink channel, send useful data by described downlink channel; By considering the information of the reception confirming described useful data, upgrade the estimation of described downlink channel, described information is sent by the receiver associated with described downlink channel.
Description
Technical field
The field of the invention is digital communication, and more accurately, is to there is the communication needing the message (knowledge) about the channel for transmitting in a small amount of environment changed in the channel.
More specifically, the present invention relates to and transmit and receive multi-carrier signal, wherein transmitter can obtain the estimation of transfer channel from the information (being also known as feedback) returned from the inverse signal of receiver.
The present invention is applied especially in single user multiple-input and multiple-output (MIMO) type transfer system or multi-user system, described Single User MIMO type transfer system such as utilizes Wave beam forming, and described multi-user system such as utilizes the technology of space division multiple access (SDMA) type.
Particularly, the present invention is applied in the transfer system meeting standard IEEE 802.11n (and meeting its version in the future especially).
Background technology
As shown in the Fig. 1 for SDMA technology, need the tranmission techniques about the message of the channel for transmitting to comprise two stages: for when not transmitting payload data, by by feedback recover about channel information, estimate the stage F of channel and the stage T for transmitting payload data.
During feedback stage, the transmitter of such as access point AP is to the station (STA#1, STA#2) of estimating down-ward link channel DL sending the grouping with pilot tone being called as " detection " and dividing into groups.Then these stations encode about the information (being written as CSI_DL) of estimated channel, and transmit this information (being written as " CSI report ") to access point AP in frame.The pattern of this channel estimating is sometimes referred to as " explicit feedback ".
During transfer phase, access point AP such as by utilizing towards the particular beam of each user, sends one or more payload grouping " DL-MU-MIMO " to multiple user.Fig. 1 shows the infrastructure elements (that is, payload data transmits grouping) of being followed by the confirmation of the reception of payload data (described confirmation is transmitted by user).Described infrastructure elements can like that often be replicated as desired, as long as channel does not change.In channel, the duration of transfer phase is determined in this change in time thus.Thus, if channel fully changes with termination effect (such as, because the interference between user has become too strong) on 25 milliseconds (ms) for SDMA technology, then the duration of transfer phase must be less than 25ms.
In the end of transfer phase, perform new feedback stage, to obtain the latest estimated of transfer channel.
Should observe thus, payload data transfer phase is longer, then total traffic data rate is larger.
However, as mentioned above, the length of second stage to be subject in channel constraint over time, and this is the movement due to transmitter or receiver, or only because some in environment moves.
Such as, be used for towards specific receiver assemble delivering power and increase the beam-forming technology of the standard 802.11n of signal to noise ratio when receiving thus, every 100ms and when not having transmitter and/or receiver mobile, perform a feedback stage in open space.
Under same environment, when using multi-user's SDMA technology, be shortened to 25ms for this cycle performing this feedback stage.
Because this cycle for performing this feedback stage has large impact for total traffic data rate, so importantly extend this cycle as far as possible, namely increase the duration of the transfer phase between two feedback stages.
There is the technology of several amendment feedback and the ratio between the duration of transfer phase for the object in order to optimize total traffic data rate.
First kind technology is the duration of being reduced feedback stage by compression channel information.However, such compression is often harmful to delivery quality.
Equations of The Second Kind technology is the duration extending transfer phase.
Such as, utilize SDMA technology, the access point AP with four antennas transmits to four user/receivers, to eliminate the interference between user in identical frequency band by forming wave beam towards each user simultaneously.Compute beam is carried out based on the channel information for each user.
Under ecotopia, each user only receives the information for this user, an empty shunting namely in the empty shunting of access point send four.
In a first mode, access point only sends the pilot frequency code element for estimating needed for the channel shunted for the sky of this user to each user thus.
However, in order to a variety of causes (comprise such as channel over time), user can receive for the information of this user, together with the interference from the information for other users.
If user has the more reception antenna of the number shunted than the sky for this user, then user can eliminate some or all information by interference cancellation techniques (such as, least mean-square error (MMSE) technology).However, only when user can estimate the channel shunted for the sky of other users, this is only possible.
In a second mode, in order to eliminate all or some interference, access point transmits to each user thus and makes user can estimate the code element of the channel shunted for the sky of this user and make each user can estimate the pilot frequency code element of the channel shunted for the sky of other users.This second pattern make may in the face of channel over time time more robust because this makes to eliminate the interference generated thus.Naturally, once interference becomes too much, just new feedback stage must be performed.
However, the defect of interference cancellation techniques is, needs to transmit multiple pilot frequency code element to each user, thus reduces the efficiency of the physical layer of transfer system.
Another defect of those technology is due to the fact that, that is, in user class, must have at least one antenna more than the sky shunting received.This causes the larger complexity of receiver and larger cost.More and more frequent at receiver must be under the prerequisite of mobile radio station, and this defect can become considerable.
So there is the demand for the novelty transmission used in transfer system and/or reception technique, it needs the message about channel when transmitting, to optimize the duration of the transfer phase between two feedback stages.
Summary of the invention
The present invention proposes the scheme of the novelty for this problem according to a kind of form by using the transmitter of at least two transmission antennas to the method using at least one receiver of at least one reception antenna transmission multi-carrier signal, the method comprises for obtaining the acquisition step that at least one transmits the estimation of downlink channel, wherein between multiple transmission antenna and (multiple) reception antenna, defines downlink channel.
According to the present invention, such method comprises transfer phase, for performing the iteration at least one times of following steps at least one downlink channel:
While the described Downlink channel estimation of consideration, described downlink channel transmits payload data; And
While considering the confirmation of reception that transmitted by the receiver associated with described downlink channel, that confirm described payload data, upgrade described Downlink channel estimation.
Thus, during the stage of transmitting payload data, the present invention proposes " initially " estimation of the renewal downlink channel using conventional channel estimation technique to carry out, such as above with reference to description of the prior art what is called " explicit feedback " technology or utilize the estimation of uplink channel and this estimation be transformed to what is called " implicit feedback " technology of downlink channel information." implicit feedback " technology should depend on that channel was the fact (that is, can estimate channel equally along a direction or other direction) of reciprocal (reciprocal), and so propose to estimate channel along uplink direction.The advantage of this technology is, performs channel estimating at transmitter place instead of at receiver place.So do not need to be estimated by return path transfer channel.However, the reciprocity of channel is only effective for the transmission between antenna, and is not effective for the signal of the simulated assembly through transmitter place and receiver place.So need calibration, the estimation carried out along uplink direction to be transformed to the estimation representing down link direction.
On the contrary, the technology of prior art depends on two difference stages, one be feedback and another be transmit payload data, only feedback stage makes it possible to estimating down-ward link channel.
By during transfer phase according to which action, in order to upgrade during feedback stage the estimation of the conventionally initial channel obtained, the invention enables the duration of the transfer phase that can extend between two feedback stages.
During the transmission of payload data, transmitter (such as, access point) while transmitting payload data, progressively (progressively) considers the channel estimating of renewal, to make to consider in channel over time thus, and be not only the initial estimation of the channel obtained during feedback stage.
Thus, when transmission is carried out, based on the new confirmation that the receiver with this channels associated transmits, again upgrade the estimation of the channel previously upgraded according to the present invention.The present invention makes to transmit Simultaneous Iteration and the progressive updating channel estimating of payload data thus.
In addition, the confirmation required for the operation of such transfer system transmitted by utilizing receiver, the present invention does not need to use any additional signal.Such as, confirmation is corresponding to the acknowledgement frame of data link layer being known as MAC layer.
When there is multiple receiver, the invention enables and by the confirmation using each receiver to transmit, the estimation of the downlink channel associated with those receivers can be upgraded.
In specific implementation of the present invention, this step of updating comprises following sub-step:
Receive described confirmation;
The uplink channel corresponding with described downlink channel is estimated based on described confirmation; With
Described Downlink channel estimation is upgraded based on described uplink channel estimation.
Thus, the invention enables the estimation of the uplink channel that may obtain according to the useful data confirmation transmitted from receiver to upgrade the estimation of downlink channel, and do not use any demand of additional signal thus.
For this purpose, the first iteration of transfer phase perform by compare the estimation and the uplink channel corresponding with downlink channel obtaining the downlink channel obtained during step estimation, determine the step of calibration factor.In addition, this step of updating also considers this calibration factor.
Thus, by considering the calibration factor of the difference between the simulated assembly that representative uses when receiving and when transmitting, the invention enables the estimation upgraded may determining reliable downlink channel based on the estimation of corresponding uplink channel.
The calibration factor also obtained after the first confirmation that reception receiver transmits thus after first of payload data transmits makes the simulated assembly may considering to use when receiving and when transmitting, and these assemblies do not relate in the reciprocity of channel.Identical by means of only aerial transmission, both receiving and transmitting.
Receiver only has in the specific implementation of the present invention of a reception antenna wherein, at least one pilot tone that the step of estimating uplink channel uses this confirmation to transmit.Under these circumstances, only there is a downlink channel and an only corresponding uplink channel between the transmitter and receiver.
Thus, the pilot tone that the present invention is utilized the information of the reception of the payload data using confirmation to be transmitted by downlink channel traditionally and transmits (such as, in channel estimating grouping (L_LTF) of the acknowledgement frame of MAC layer), to estimate the uplink channel corresponding with downlink channel.
Receiver comprises at least two reception antennas and in another specific implementation of the present invention wherein according to the form confirmation of receipt of the acknowledgement frame of MAC layer wherein, this acknowledgement frame comprises channel estimating grouping (L_LTF) of carrying two pilot set, each pilot set associates with the difference reception antenna of receiver, based on the pilot set associated with uplink channel, each uplink channel is performed to the step of estimating uplink channel.
Thus, use and there is the confirmation that single channel estimates grouping, the invention enables and may estimate and each uplink channel that each antenna of receiver associates.Confirmation packets of information under such circumstances draws together its each pilot set associated with corresponding uplink channel, and when receiving this confirmation, transmitter can distinguish the pilot set associated with each uplink channel, to estimate each in those uplink channels.
In another specific implementation of the present invention, according to the form confirmation of receipt information of the acknowledgement frame of MAC layer, this confirmation comprises the distinct channel associated with each reception antenna of described receiver and estimates divide into groups (HT_LTF1 and HT_LTF2).Then divide into groups based on the channel estimating associated with the reception antenna of definition uplink channel, uplink channel estimation step is performed for each uplink channel.
The present invention makes thus may based on comprising the grouping of multiple channel estimating (such as, the grouping of channel estimating is used for each channel associated with each antenna of receiver) confirmation, estimate and each uplink channel that each antenna of receiver associates.When transmitter confirmation of receipt information, each uplink channel can be estimated based on the channel estimating grouping of difference association.
In particular aspects of the present invention, the step of estimating uplink channel transmits the estimation of the Part I of the frequency response of uplink channel, and this transfer approach comprises and makes it possible to estimate the frequency of the Part II of described frequency response and/or temporally interpolated step from described Part I.
Thus, in some cases, such as, when not transmitting payload data by the frequency band identical with confirmation, confirmation makes can not the whole frequency response of estimating uplink channel.The present invention then make can by based on the frequency response estimated according to confirmation a part, utilize the Interpolation across frequency that may associate with temporal interpolation, this of frequency response obtaining uplink channel estimate completely.
Present invention also offers a kind of transmitter, for transmitting multi-carrier signal at least one receiver of at least one reception antenna of use, described transmitter uses at least two transmission antennas, and comprise for obtaining the parts that at least one transmits the estimation of downlink channel, wherein between one of one of described transmission antenna and described reception antenna, define downlink channel.
According to the present invention, such transmitter also comprise according to an iteration form at least one downlink channel be at least activated once with lower component:
For when considering described Downlink channel estimation, on described downlink channel, transmit the parts of payload data; And
For the parts by considering confirmation that transmitted by the receiver associated with described downlink channel, that confirm the reception of described payload data, upgrading described Downlink channel estimation.
Such transmitter is particularly suitable for performing above-described transfer approach.Exemplarily, it can be the access point of WiFi network.
Another aspect provides a kind of for receive with by using the transmitter transmission of at least two transmission antennas and by the method for reseptance of signal corresponding to the multi-carrier signal using the receiver of at least two reception antennas to receive.
According to the present invention, such method of reseptance comprises: for the iteration at least one times of the following steps of at least two downlink channel, wherein between one of one of described transmission antenna and described reception antenna, defines downlink channel:
Described downlink channel receives payload data; With
Generate and transmit confirmation, this confirmation confirms the reception of described payload data and makes described transmitter can estimate the uplink channel corresponding with described downlink channel.
Thus, the invention enables and by utilizing confirmation required for the operation of such transfer system, that to be generated by receiver and transmit, the uplink channel corresponding with the antenna of receiver can be estimated, and thus without any need for additional signal.
Such as, in specific implementation of the present invention, this generation step is according to being known as the form of acknowledgement frame of data link layer of MAC layer to generate described confirmation, and described confirmation comprises channel estimating grouping (L_LTF) with at least two pilot set, and each pilot set associates with the difference reception antenna of described receiver.
Of the present invention in a certain respect in, arrange the pilot tone of described pilot set in such a manner, make transmit confirmation step during, transmitted the pilot tone of given frequency at any given time by the single antenna in described reception antenna.
At access point place, owing to being orthogonal with the pilot set that antenna associates, so detect them separately, to make to estimate each uplink channel.
Thus, comprise single channel and estimate that the confirmation of grouping makes may estimate and each uplink channel that each antenna of receiver associates.
In realizing second, described generation step according to be known as MAC layer data link layer acknowledgement frame Form generation described in confirmation, and described confirmation comprises the distinct channel associated with each reception antenna of described receiver estimates divide into groups (HT_LTF1 and HT_LTF2).
Thus, confirmation comprises multiple channel estimating grouping (such as, each channel for associating with each antenna of receiver), and each grouping makes to estimate corresponding uplink channel.
Should observe in this implementation, still transmit except the grouping (HT_LTF1 and HT_LTF2) except associating with each receiver antenna of receiver " tradition " channel estimating divide into groups (L_LTF) time, keep the compatibility with comparatively early standard.
In particular aspects of the present invention, described generation step is according to the Form generation confirmation of acknowledgement frame of data link layer being known as MAC layer, and described transfer step transmits at least Part I of described acknowledgement frame on 40 megahertzes (MHz) frequency band, and in due course, two 20MHz frequency bands transmit the Part II of described acknowledgement frame.
Thus, according to some situation of ad hoc fashion process (such as, wherein do not transmit payload data by the frequency band identical with confirmation), make it possible in the estimation not needing to carry out in the frequency at access point place and/or temporally interpolated situation each uplink channel.
In these cases, first scheme is to send acknowledgement frame by the frequency band identical with payload data.
Alternative plan is the part (Part I) only being sent acknowledgement frame by the frequency band identical with useful data, makes it possible to thus estimate channel, and makes to maximize with the compatibility of existing station and comparatively early standard.
Such as, Part I may correspond to and divides into groups at least one channel estimating.
The present invention also provides a kind of receiver, and for the signal that the multi-carrier signal received with use the transmitter of at least two transmission antennas to transmit is corresponding, described receiver uses at least two reception antennas.
According to the present invention, such receiver comprises: at least two downlink channel according to iteration form at least activate once with lower component, wherein between one of one of described transmission antenna and described reception antenna, define downlink channel:
For receiving the parts of payload data on described downlink channel; With
For generating the parts of confirmation and the parts for transmitting confirmation, this confirmation confirms the reception of described payload data, makes described transmitter may estimate the uplink channel corresponding with described downlink channel.
Such receiver is particularly suitable for performing above-described method of reseptance.Exemplarily, it can be to provide the station of the set of basic in WiFi network.
This receiver can comprise the various characteristics relevant to method of reseptance of the present invention naturally.Thus, the characteristic of this receiver is identical with advantage with the characteristic of this method of reseptance with advantage, and does not describe them in more detail.
Another aspect provides a kind of confirmation signal by using the receiver of at least two reception antennas to transmit, this signal pin is to the transmitter using at least two transmission antennas.
According to the present invention, such confirmation signaling bearer confirmation, this confirmation confirms the reception of the payload data that described transmitter transmits via at least two downlink channel, downlink channel is defined between one of one of described transmission antenna and described reception antenna, the reception of payload data described in described validation of information, makes described transmitter can estimate the uplink channel corresponding with described downlink channel.
Transmission of the present invention and method of reseptance can realize according to various mode, particularly realize according to hard wire version or software form.
In another aspect, the invention provides a kind of computer program, when processor runs this program, this program comprises the instruction being suitable for realizing above-described transfer approach and/or method of reseptance.Such program can use any programming language.This program can be able to record on a computer-readable medium from downloaded and/or this program.
Accompanying drawing explanation
By reading following description and the accompanying drawing of the specific implementation only provided as illustrative and non-limiting example, other characteristics of the present invention and advantage more clearly occur, wherein:
Fig. 1 shows in prior art SDMA technology the example in the stage needed for transmitting for data;
Fig. 2 shows the key step of transfer approach in the present implementation;
Fig. 3 shows the example of the acknowledgement frame of MAC layer of the prior art;
Fig. 4 shows the example of the subcarrier distribution for payload data signal and confirmation signal of the prior art;
Fig. 5 shows the example of the confirmation in realization of the present invention;
The example that Fig. 6 a and 6b respectively illustrates the acknowledgement frame of MAC layer of the prior art and the example of acknowledgement frame revised in the present implementation; With
Fig. 7 shows the structure of the transmitter in specific embodiment of the present invention.
Embodiment
5.1 General Principle
The invention reside in the environment that there is a small amount of change in the channel, need the context of the transmission of the message about transfer channel when transmitting.Traditionally, by the estimation of channel obtained during feedback stage before transferring data, and obtain this channel massage when transmitting, this feedback stage is periodically performed can consider the change of channel.
General Principle of the present invention is action during data transmit, and to upgrade the estimation of the downlink channel between transmitter and receiver, makes the duration of the transfer phase may optimized between two feedback stages thus.
In order to so do, the confirmation of the reception for confirming the payload data that transmitter transmits that the present invention uses receiver to transmit, to upgrade the estimation of downlink channel.
Thus, owing to upgrading channel estimating during payload data transfer phase, so before must realizing new feedback stage, the duration of transfer phase can be extended, because the new channel estimating upgraded is considered in the transmission of payload data.
According to which, the invention enables the ratio may optimized between the duration of feedback stage and the duration of transfer phase, optimize total traffic data rate thus.
5.2 descriptions realized
Here is the description of the key step with reference to the transfer approach in the realization of the present invention of figure 2.
For comprising the transmitter of use at least two transmission antennas and using the transfer system of at least one receiver of at least one reception antenna to consider.
In this realization of the present invention, this transfer approach comprises at least one downlink channel between the antenna of transmitter and the antenna of receiver, obtains the step 21 of the estimation CSI_DL of downlink channel.This step 21 such as use conventional channel estimation technique (such as, as above with reference to description of the prior art what is called " explicit feedback " technology or use uplink channel estimation and this estimation be transformed to what is called " implicit feedback " technology of downlink channel information) realize.Exemplarily, this step 21 corresponds to above-mentioned feedback stage F.
During each step 221 of execution be described below and 222 transfer phase 22 at least one times, upgrade initial this channel estimating CSI_DL obtained subsequently.
First, when considering channel estimating CSI_DL (the channel estimating CSI_DL initially obtaining in step 21 when performing the first iteration of transfer phase 22 or previously upgraded according to the present invention when performing the i-th iteration of transfer phase 22), perform the step 221 that payload data transmits E.
In order to verify the reception of the payload data transmitted during step 221, receiver transmission confirms the validity the confirmation ACK of the reception of load data.
This confirmation is used, to upgrade channel estimating CSI_DL during the step 222 upgrading MAJ in this realization of the present invention.
Then, in the period such as ensuing iteration of transfer step 221, consider that the channel estimating CSI_DL of this renewal is for transmitting following payload data.
More accurately, the step 222 upgrading MAJ channel estimating CSI_DL realizes the confirmation ACK transmitted based on receiver, the step estimating the uplink channel (be also referred to as UL) corresponding with downlink channel.
This estimating step transmission is written as the uplink channel estimation information of CSI_UL.
With reference to figure 3,4,5,6a and 6b, here is the description of several modification of this realization of the present invention from payload data confirmation estimating uplink channel.
Thereafter be upgrade the description of the realization of the present invention of Downlink channel estimation based on corresponding uplink channel estimation and how to use upgraded channel estimating for transmitting the description of payload data below.
5.3 estimating uplink channels in one implementation
5.3.1 the first modification: the receiver with an antenna
First customized configuration is considered, wherein receiver only uses a reception antenna, and wherein come to transmit via uplink channel to confirm at upper this antenna that uses of the frequency band (such as, 20MHz) that the payload data transmitted via corresponding downlink channel with transmitter is identical.
In the configuration, " tradition " acknowledgement frame shown in Fig. 3 can be used.Such as, in 802.11 standards, transmitter can use the pilot tone leaving over transmission in long training field (L-LTF) to estimate the uplink channel corresponding with the downlink channel of its transmission payload data.
In the example shown in fig. 3, field L-LTF is made up of the pilot tone transmitted on each subcarrier of multicarrier payload data confirmation signal (set of pilot tone T1, is replicated to T2=T1).
Also wherein receiver is only used to a reception antenna and wherein on the frequency band different with the frequency band of the payload data that transmitter transmits, transmits the second customized configuration confirmed by described antenna and consider.
Exemplarily, when transmitting payload data via downlink channel and transmit confirmation via corresponding uplink channel in 40MHz frequency band in 2 × 20MHz frequency band, this customized configuration can be met with in 802.11n or 802.11ac standard.Under these circumstances, the subcarrier of multicarrier payload data signal is distributed not in accordance with the mode identical with the subcarrier of multicarrier confirmation signal, as shown in Figure 4.
Thus, can be observed, for 40MHz frequency band, distribute 128 subcarriers used as follows:
114 subcarriers are suitable for use in the pilot tone P estimating channel (or being suitable for payload data); With
14 subcarriers are modulated by null value (being called as sky subcarrier); wherein three (DC) is positioned at the centre of frequency band; and other (protection subcarrier GI) are positioned at the both sides of frequency band, so that restriction is overlapping with using other spectrums applied of nearby frequency bands.
On the contrary, for 2 × 20MHz frequency band, distribute 128 subcarriers used as follows:
104 subcarriers are the pilot tone P being suitable for estimating channel (or being suitable for payload data); With
24 subcarriers are sky subcarriers; wherein two (DC) is positioned at the centre of each 20MHz frequency band; and other (protection subcarrier GI) are positioned at the both sides of each 20MHz frequency band, so that restriction is overlapping with using other spectrums applied of nearby frequency bands.
Thus, can see, can not for uplink channel direct estimation 11 subcarriers.
Such as, estimate two empty subcarriers of the centre of each 20MHz frequency band from adjacent sub-carriers by Interpolation across frequency.
On the contrary, for nine subcarriers of centre being positioned at 40MHz frequency band, Interpolation across frequency is not enough to estimate them.
First scheme is to realize Interpolation across frequency, as shown in the square frame in figure while the subcarrier of " good " side only using 20MHz frequency band.When estimating to lose subcarrier, this Interpolation across frequency can associate with temporal interpolation, to utilize more coherent elements.The advantage of this first scheme is to avoid revising " tradition " acknowledgement frame shown in Fig. 3.
Alternative plan is, by replacing 2 × 20MHz, transmission " tradition " acknowledgement frame according to 40MHz or at least transmitting the pilot frequency code element being used for channel estimating, to revise this " tradition " acknowledgement frame.However, the program still less than the early version with this standard (such as, version 802.11a) completely compatible, and the program may be punished (penalizing) personated old man and become station, and this personated old man becomes station then to need to wait for longer than other stations before turning back to the competitive stage.When can not detect the data division of transmission when standing (this will occur in this case); confirm that protection comes into force (putintoplace), and standing in of just discussing must wait for (correspond to transmit confirm) duration before can turning back to the competitive stage.Because the grouping just discussed confirms, so this grouping is not oneself be identified to follow, but it was directly followed by the competitive stage.The station of another duration confirmed is waited for so will sternly be punished after the transmission confirmed.
However, can advantageously use the program be used for except stop transfer phase basic element confirmation except all confirmations, as described above with reference to Figure 1.
Third program is the field L-LTF only transmitting acknowledgement frame according to 40MHz, transmits the remainder of acknowledgement frame according to 2 × 20MHz simultaneously.The program makes to keep the compatibility with the early version of this standard.
5.3.2 the second modification: the receiver with multiple antenna
Under regard to wherein each station and there is more than one antenna and the configuration that can receive multiple stream according to sky point mode is considered.
The invention enables the downlink channel may estimated for each empty shunting.
This channel estimation phase (such as using feedback technique) relates to the special pilot transmitted for each empty shunting, to estimate the channel it transmitting empty shunting.
However, only in an empty shunting, transmit " tradition " to confirm, that is, only use an antenna, or only estimating to use while " equivalent single antenna channel " (such as, via field L-LTF) multiple antenna (as just used only an antenna).
The present invention proposes several scheme, be provided for the downlink channel may estimated for each empty shunting.
Under regard to the example that wherein receiver has two antennas and consider.
First scheme is to transmit while use two antennas to confirm: use the first antenna (STA1) to transmit each other payload subcarrier (P), and use the second antenna (STA2) to transmit other subcarriers, (only transmit solid line subcarrier) as shown in Figure 5.
The confirmation (ACK) transmitted comprises pilot tone (2 × 24P) and the unloaded ripple (1DC, 6GI and 5GI) of some number thus.
At access point place, by distinguishing the subcarrier representing each channel, estimate and the uplink channel that two antennas associate.
Thus, access point uses representative from the first half of the subcarrier of the channel of antenna STA1, to estimate the channel associated with antenna STA1, and uses representative from the later half of the subcarrier of the channel of antenna STA2, to estimate the channel associated with antenna STA2.Under these circumstances, the position to the access point notice subcarrier corresponding with different antennae is needed.Simple mode defines the transfer mode applying the program in a standard, and signal the use of this pattern in the beacon of broadcasting in signaling field in each lead code transmitted or at access point.
Should observe, need to perform Interpolation across frequency, to estimate the subcarrier that antenna does not transmit.Can perform in a frequency domain this interpolation (linear interpolation, MMSE ...), or by transform to transfer (transfer) territory perform this interpolation (use discrete Fourier transform (DFT) (DFT) or discrete cosine transform (DCT) ...)
Access point carries out this estimation for its each antenna, to estimate the uplink channel (CSL_UL) corresponding with downlink channel.In two-antenna configuration, access point recovers the pilot tone transmitted by the subcarrier corresponding with the first antenna (or respectively second), estimate the channel on those each subcarriers, and applying frequency interpolation is to estimate the channel on the subcarrier corresponding with the second antenna (or respectively first).
Can by consider often N number of in a subcarrier (instead of each other subcarrier), this example is generalized to the antenna that number is N.
Alternative plan is to revise acknowledgement frame, to make it possible to estimate multiple uplink channel.
In order to do like this, such as in physical layer convergence procedure (PLCP) lead code, (Fig. 6 is a) middle inserts field HT-LTF, as shown in Figure 6b.These fields (HT-LTF1 with HT-LTF2) are respectively used to estimate the uplink channel associated with antenna STA1 and the uplink channel associated with antenna STA2.
The operation of field HT-LTF and code element can meet standard IEEE P802.11n/D11.0DraftstandardforInformationTechnology-Tele communicationsandinformationexchangebetweensystems – Localandmetropolitanareanetworks-SpecificrequirementsPar t11:WirelessLANMediumAccessControl (MAC) andPhysicalLayer (PHY) specificationsAmendment5:EnhancementsforHigherThroughput, Chapter20.3.9.4.6.
However, this alternative plan early version (such as, version 802.11a) that is incomplete and this standard is compatible, and can punish older generation station, because needs were waited for longer, as explained above than other stations by they before turning back to the competitive stage.Can advantageously use the program be used for except stop transfer phase basic element confirmation except all confirmations, as described above with reference to Figure 1.
5.4 in one implementation, uses uplink channel estimation to upgrade corresponding Downlink channel estimation
5.4.1 Downlink channel estimation is upgraded
Here may be used on a kind of description realized of the present invention, how upgrades the estimation CSI_DL of downlink channel from the estimation CSI_UL of corresponding uplink channel, as obtained in the manner described above.
Should wander back to, in digital, estimate that channel considers the simulated assembly of transmitter, the simulated assembly by aerial transmission and receiver.By means of only aerial transmission in the two directions (such as, for uplink channel UL and downlink channel DL) identical.So the response of the simulated assembly in uplink channel and downlink channel must be calibrated, to obtain the outstanding reciprocity being used for this channel.
Thus, should observe, (as mentioned above, obtaining from confirmation in the present invention) uplink channel estimation CSI_UL and Downlink channel estimation CSI_DL has a little difference.
So, must calibration factors being considered, the uplink channel estimation CSI_UL for upgrading downlink channel CSI_DL can be used, and considering the Downlink channel estimation CSI_DL of this renewal when transmitting payload data.
Think that Downlink channel estimation CSI_DL can write as follows:
CSI_DL＝F
DLR×H
DL×F
DLE
Wherein H
dLthe matrix of the coefficient representing channel, F
dLRthe matrix of the coefficient of analog filter when being representative reception, and F
dLEthe matrix of the coefficient of analog filter when being representative transmission.
According to identical mode, uplink channel estimation CSI_UL can write as follows:
CSI_UL＝F
ULR×H
UL×F
ULE
Wherein H
uLthe matrix of the coefficient representing channel, F
uLRthe matrix of the coefficient of analog filter when being representative reception, and F
uLEthe matrix of the coefficient of analog filter when being representative transmission.
In addition, known:
H
uL=H
dL -1, F
dLR≠ F
uLR, and F
dLE≠ F
uLE
Initially suppose during the first iteration of transfer phase, namely during first of payload data transmits, after the step such as being estimated channel by feedback technique, also do not revise channel, and each user only receives the data (that is, wave beam does not generate any interference) transmitted by the wave beam of this user.Under these circumstances, the difference between the Downlink channel estimation CSI_DL that obtains of the uplink channel estimation CSI_UL that obtains of the present invention and feedback technique corresponds to the difference between the filter of representative simulation assembly.
Thus, based on CSI_UL and CSI_DL, calibration may be performed to obtain calibration factor F
cAL, make:
CSI_UL×F
CAL＝CSI_DL
The example of collimation technique is provided in standard IEEE P802.11n/D11.0DraftstandardforInformationTechnology-Tele communicationsandinformationexchangebetweensystems-Local andmetropolitanareanetworks-SpecificrequirementsPart11:W irelessLANMediumAccessControl (MAC) andPhysicalLayer (PHY) specificationsAmendment5:EnhancementsforHigherThroughput, Chapter20.3.12.1.
Then this calibration factor F is used in the present invention
cALfor upgrading Downlink channel estimation based on uplink channel estimation.
Thus, by uplink channel estimation is multiplied by calibration factor, obtain upgraded Downlink channel estimation:
CSI_DL=CSI_UL × the F upgraded
cAL
Should wander back to, each transmission based on receiver confirms, carrys out iteration and realizes this step of updating, to confirm the reception of the payload data that transmitter transmits.
Thus, by considering the different value of the uplink channel estimation obtained during previous ones or passing through to perform linear prediction, the renewal of Downlink channel estimation can be optimized.
Such as, can specify, with time of implementation interpolation on N previous ones.
Upgrade
Then upgraded Downlink channel estimation can be used, for transmitting following payload data, such as, so that reconstruct is used for the wave beam that SDMA transmits.All SDMA technology utilize CSI_DL matrix in their wave beam calculates.
The present invention makes to obtain the Downlink channel estimation CSI_DL of renewal thus and uses it for constructing new wave beam.
5.4.2 payload data transfer phase duration/end of iteration
As mentioned above, the present invention makes to extend through the duration between two stages that the calibration factor that utilizes the estimation of corresponding uplink channel and determine during the first iteration of each transfer phase carrys out estimating down-ward link channel, payload data transfer phase thus.
However, after measuring sometime and having pass by, (such as, when the step by means of the present invention's more new estimation no longer can consider the real change of channel) new channel estimation phase must be realized.
Thus, may before continuation transmit payload data, definition upgrades threshold value, exceeds the stage that this threshold value then must perform estimating down-ward link channel.
Exemplarily, this threshold value can represent the difference between present downlink channel estimation with the Downlink channel estimation upgraded.Thus, when this difference becomes too large (that is, when the change in channel is too large), perform the new stage of estimating down-ward link channel.
Similarly, the calibration factor of the difference between simulated assembly when representative transmits and receives calculates during the first iteration of each transfer phase, does not consider the change (such as, due to simulated assembly heating) of the calibration that can occur during transmitting.
The criterion relevant to calibration factor may be defined thus, as the function performing the new stage of estimating down-ward link channel before continuing to transmit payload data.Such as, this criterion can be outside criterion, and it is by temperature sensor transmission and the change of representative simulation assembly, and result represents the change of calibration factor.
The present invention also prepares other threshold value of interference level observed by the receiver in consideration system.Thus, when the rank that the interference received together with the signal sent to receiver observed by receiver exceeds a certain threshold value, such as, when changing environment (such as, because forward neighboring user transmits new signal), receiver such as can signal this event in confirmation.Under these circumstances, before continuation transmits payload data, the new Downlink channel estimation stage is performed, to consider the interference in channel estimating.
Finally, if transmitter no longer has any payload data that will transmit in a certain length of time, then preferably realize new channel estimation phase, instead of transmit following payload data based on the estimation upgraded according to the present invention.When transmitter no longer transmits payload data, such as, perform feedback stage and do not punish total transfer rate.
5.5 realizations of the present invention
The present invention also can perform in the context of the SDMA technology of execution first and second pattern with reference to description of the prior art.
In the second pattern for eliminating the interference between user, access point transmits pilot frequency code element to each user, make user can estimate the channel of the sky shunting for it, together with the pilot frequency code element making them can estimate the channel shunted for the sky of other users thus.This second pattern can be robust for channel over time, because this second pattern can eliminate the interference of generation.
Under these circumstances, the invention enables the estimation that may obtain the renewal of downlink channel before execution second pattern, interference can be eliminated based on reliable channel estimating (because this channel estimating is updated according to the present invention), instead of depend on initial channel estimation that obtain at feedback stage, that no longer represent the channel through being disturbed.
The judgement changed between two patterns can be made by access point, such as, consider the uplink channel CSI_UL obtained according to the present invention.
In a further implementation, the judgement of the transformation performed between two patterns can be made by receiver.Under these circumstances, need to revise acknowledgement frame, to create the field that this pattern of carrying changes information.Such as, the signaling bit of (form according to the newer field in acknowledgement frame) in (according to the form of information hidden in filling bit, such as, as description in No. 08/57014, patent documentation) or MAC layer in physical layer.
The structure of 5.6 transmitters
Finally, with reference to figure 7, here is the description of the simplified structure for the transmitter in above-mentioned specific implementation.
Such transmitter has the memory 71 and processor unit 72 that are made up of buffer memory, and processor unit 72 is such as equipped with microprocessor μ P, and is controlled by the computer program 73 performing transfer approach of the present invention.
When initialization, the code command of computer program 73 can such as be loaded onto in random access memory (RAM) before the processor by processor unit 72 runs.Processor unit 72 receiving downlink channel estimating CSI_DL is as input.The microprocessor of processor unit 72 performs the step of the above-mentioned transfer approach of the instruction of according calculation machine program 73, to upgrade Downlink channel estimation CSI_DL.For this purpose, except buffer memory 71, transmitter comprise estimate for Downlink channels under consideration while transmit on a downlink channel payload data parts and for by considering that the information of the reception confirming the payload data transmitted by the receiver associated with downlink channel upgrades the parts of Downlink channel estimation.These parts are by the Microprocessor S3C44B0X of processor unit 72.
Claims (11)
1. one kind for by using the transmitter of at least two transmission antennas to transmit the method for multi-carrier signal to using at least one receiver of at least one reception antenna, the method comprises: obtain step, for obtaining the estimation CSI_DL that at least one transmits downlink channel, wherein between described transmission antenna and described reception antenna, define downlink channel;
The method is characterized in that it comprises transfer phase, for at least one downlink channel, perform the iteration at least one times of following steps:
While the described Downlink channel estimation of consideration, described downlink channel transmits payload data; And
Upgrade described Downlink channel estimation based on uplink channel estimation, this uplink channel corresponds to described downlink channel,
Described step of updating comprises following sub-step:
Receive confirmation that transmitted by the receiver associated with described downlink channel, that confirm the reception of described payload data;
This uplink channel is estimated based on described confirmation,
The step of described estimating uplink channel transmits the estimation of the Part I of the frequency response of described uplink channel, and described method comprises and makes it possible to estimate the Part II of described frequency response from described Part I and upgrade the frequency of described Downlink channel estimation and/or temporally interpolated step based on described uplink channel estimation.
2. transfer approach according to claim 1, it is characterized in that, the first time iteration of this transfer phase performs by the estimation of the estimation and the described uplink channel corresponding with described downlink channel of comparing the described downlink channel obtained during described acquisition step, the step determining calibration factor, and it is characterized in that, described step of updating also considers described calibration factor.
3. transfer approach according to claim 1, it is characterized in that, described receiver has at least two reception antennas, described confirmation according to be known as MAC layer data link layer acknowledgement frame form receive, described confirmation comprises the channel estimating grouping L_LTF of carrying two pilot set, each pilot set associates with the difference reception antenna of described receiver, and it is characterized in that, based on the pilot set associated with uplink channel, uplink channel described in each is performed to the step of described estimating uplink channel.
4. transfer approach according to claim 1, it is characterized in that, described confirmation according to be known as MAC layer data link layer acknowledgement frame form receive, described confirmation comprises the distinct channel associated with each reception antenna of described receiver and estimates HT_LTF1 and HT_LTF2 that divide into groups, and it is characterized in that, divide into groups uplink channel described in each is performed the step of described estimating uplink channel based on the channel estimating associated with the reception antenna of the described uplink channel of definition.
5. a transmitter, for transmitting multi-carrier signal at least one receiver of at least one reception antenna of use, described transmitter uses at least two transmission antennas, and comprise for obtaining the parts that at least one transmits the estimation of downlink channel, wherein between one of one of described transmission antenna and described reception antenna, define downlink channel;
The feature of this transmitter is, it also comprise according to an iteration form at least one downlink channel be at least activated once with lower component:
For when considering described Downlink channel estimation, on described downlink channel, transmit the parts of payload data; And
For based on correspond to described downlink channel uplink channel estimation, upgrade the parts of described Downlink channel estimation,
The described parts for upgrading comprise with lower component:
For receiving parts that transmitted by the receiver associated with described downlink channel, that confirm the confirmation of the reception of described payload data;
For estimating this uplink channel based on described confirmation and transmitting the parts of the estimation of the Part I of the frequency response of described uplink channel,
And described transmitter comprise make it possible to from described Part I estimate the Part II of described frequency response for frequency and/or temporally interpolated parts.
6. one kind for receive with by using the transmitter transmission of at least two transmission antennas and by the method for reseptance of signal corresponding to the multi-carrier signal using the receiver of at least one reception antenna to receive;
The method is characterized in that, it comprises: to the iteration at least one times of the following steps of at least two downlink channel, wherein between one of one of described transmission antenna and described reception antenna, defines downlink channel:
Described downlink channel receives payload data; With
Generate and transmit confirmation, this confirmation confirms the reception of described payload data and makes described transmitter can estimate the uplink channel corresponding with described downlink channel,
Described transmitter transmits the estimation of the Part I of the frequency response of described uplink channel, and carries out the frequency and/or the temporal interpolation that make it possible to estimate the Part II of described frequency response from described Part I.
7. method of reseptance according to claim 6, it is characterized in that, described generation step according to be known as MAC layer data link layer acknowledgement frame Form generation described in confirmation, and described confirmation comprises the channel estimating grouping L_LTF with at least two pilot set, and each pilot set associates with the difference reception antenna of described receiver.
8. method of reseptance according to claim 7, it is characterized in that, arrange the pilot tone of described pilot set in such a manner, make, during the step of described transmission confirmation, to be transmitted the pilot tone of given frequency at any given time by the single antenna in described reception antenna.
9. method of reseptance according to claim 6, it is characterized in that, described generation step according to be known as MAC layer data link layer acknowledgement frame Form generation described in confirmation, and described confirmation comprises the distinct channel associated with each reception antenna of described receiver estimates HT_LTF1 and HT_LTF2 that divide into groups.
10. method of reseptance according to claim 6, it is characterized in that, described generation step according to be known as MAC layer data link layer acknowledgement frame Form generation described in confirmation, and it is characterized in that, described transfer step transmits at least Part I of described acknowledgement frame on 40MHz frequency band, and in due course, two 20MHz frequency bands transmit the Part II of described acknowledgement frame.
11. 1 kinds of receivers, for the signal that the multi-carrier signal received with use the transmitter of at least two transmission antennas to transmit is corresponding, described receiver uses at least two reception antennas;
The feature of this receiver is, it comprises: at least two downlink channel according to iteration form at least activate once with lower component, wherein between one of one of described transmission antenna and described reception antenna, define downlink channel:
For receiving the parts of payload data on described downlink channel; With
For generating the parts of confirmation and transmitting the parts of confirmation, this confirmation confirms the reception of described payload data, makes described transmitter may estimate the uplink channel corresponding with described downlink channel,
Described transmitter transmits the estimation of the Part I of the frequency response of described uplink channel, and carries out the frequency and/or the temporal interpolation that make it possible to estimate the Part II of described frequency response from described Part I.
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| US11108442B1 (en) * | 2018-07-20 | 2021-08-31 | Qualcomm Incorporated | Calibration and implicit sounding using multi user multiple input multiple output transmissions |
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| CN102986144A (en) | 2013-03-20 |
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| US20130051242A1 (en) | 2013-02-28 |
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